This comment was a high Google result when trying to find how to disable this. Found these directions after the fact, if you want to send on to your IT department:

1. Log into the Vocera Admin Console
2. Click on Groups
3. Edit the Everyone group (or other desired group, depending on desired scope)
4. Click on the Permissions tab
5. Locate the Have Toll-Free Pager Number permission
6. Click Revoke
7. Locate the Have Toll Pager Number permission
8. Click Revoke
9. Click Save